CN110817827A

CN110817827A - Method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid

Info

Publication number: CN110817827A
Application number: CN201810907000.8A
Authority: CN
Inventors: 吴正奇; 姚其凤; 李摇摇; 许琦; 徐歆; 吴龙; 李倩; 陈小强
Original assignee: Hubei University of Technology
Current assignee: Hubei University of Technology
Priority date: 2018-08-09
Filing date: 2018-08-09
Publication date: 2020-02-21

Abstract

The invention discloses a method for preparing food-grade potassium dihydrogen phosphate by using industrial wet-process purified phosphoric acid, which comprises the steps of ⑴ diluting with water, putting the industrial wet-process purified phosphoric acid into an acid-resistant container, adding pure water, stirring and diluting, ⑵ neutralizing reaction and defluorination, adding a defluorination and desulfurization agent and potassium hydroxide, stirring and reacting, membrane filtration to obtain a precisely filtered neutralizing solution, ⑶ oxidizing and dearsenifying and slightly alkaline heavy metal removal and membrane filtration, adjusting the pH value of the neutralizing solution to be slightly alkaline, adding an oxidant, heating, cooling and membrane filtration to obtain a precisely filtered slightly alkaline heavy metal removal and oxidized dearsenification solution, ⑷ pH adjustment and concentration, adjusting the pH value with phosphoric acid and concentrating to obtain a potassium dihydrogen phosphate concentrated solution, ⑸ cooling crystallization, transferring the concentrated solution into a crystallization device, stirring, cooling, crystallizing and solid-liquid separation to obtain potassium dihydrogen phosphate wet crystals, ⑹ crystallizing and drying, drying the wet crystals to obtain the product requiring moisture, thus obtaining the food-grade potassium dihydrogen phosphate product.

Description

Method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid

Technical Field

The invention relates to the technical field of food additive processing, in particular to a method for preparing food-grade monopotassium phosphate by purifying phosphoric acid by an industrial wet method.

Background

The potassium dihydrogen phosphate is an important chemical raw material and is widely applied to industrial departments such as biological fermentation, food, medicine, chemical industry, feed, agriculture and the like. The method for producing potassium dihydrogen phosphate mainly includes a neutralization method, an extraction method, an ion exchange method, a double decomposition method, a direct method, a crystallization method, an electrolytic method, and the like, and the main production method is the neutralization method. Phosphoric acid can be divided into wet-process phosphoric acid obtained by acidifying phosphate ore as a raw material and hot-wet-process phosphoric acid obtained by burning pure phosphorus as a raw material according to the source of the phosphoric acid, so potassium dihydrogen phosphate can be divided into hot-process potassium dihydrogen phosphate and wet-process potassium dihydrogen phosphate, wherein the hot-process potassium dihydrogen phosphate has high purity but high cost; according to the purity, the monopotassium phosphate can be divided into industrial grade, agricultural grade and food grade, wherein the food grade monopotassium phosphate has the highest quality standard. Food grade monopotassium phosphate is typically produced from hot process phosphoric acid via a neutralization process.

The method has the advantages that the method has abundant phosphate ore resources in China, industrial-grade wet-process phosphoric acid and phosphate represented by potassium dihydrogen phosphate are prepared by using the phosphate ore as a raw material, the technology is mature, the cost is low, the product quality is stable, the impurity content is high, the purity is low, and the requirement of food grade cannot be met. In contrast, the production of thermal phosphoric acid and its phosphates represented by potassium dihydrogen phosphate from phosphorus has a high cost, although the technology is mature, the product quality is stable, the purity is high, and the impurity content is low, which can meet the requirements of food grade. Therefore, how to utilize rich phosphate rock resources in China to prepare food-grade phosphoric acid and phosphate represented by potassium dihydrogen phosphate through wet-process phosphoric acid is economically important and urgent in demand.

The core problem to be solved for preparing the food-grade monopotassium phosphate by using wet-process phosphoric acid (comprising a diluted phosphoric acid semi-finished product with the mass percentage concentration of 20-50% and industrial wet-process purified phosphoric acid with the mass percentage concentration of 75% and 85%) as a raw material comprises the following steps: a. how to separate a small amount of toxic elements such as lead, cadmium, mercury and arsenic in industrial wet-process phosphoric acid to ensure that the product meets the necessary sanitary and safety requirements of food additives; b. how to separate fluorine, iron, calcium and other conventional elements in the industrial wet-process phosphoric acid to ensure that the product reaches the corresponding quality limit index; c. how to separate solid particles, pigment particles and the like in industrial wet-process phosphoric acid to ensure that each index of a product reaches corresponding quality requirements. A large number of researchers at home and abroad research the process technology for preparing food-grade phosphoric acid by refining and purifying wet-process phosphoric acid and preparing food-grade phosphate represented by monopotassium phosphate by taking the wet-process phosphoric acid as a raw material, and a batch of new processes, new technologies and new achievements are brought forward. For example, Hubei Sanning chemical company develops a new technology which is mainly characterized by obtaining food-grade potassium dihydrogen phosphate by extracting wet-process phosphoric acid from melamine, back-extracting and potassium chloride potassizing, and realizes industrialization. Chinese patent CN93114914.2 discloses a new method for preparing potassium dihydrogen phosphate by a medium-temperature double decomposition oxidation precipitation method; chinese patent CN86101186.4 discloses a method for preparing potassium dihydrogen phosphate by an "association-displacement" method; US7601319 discloses a process for the production of monopotassium phosphate.

How to remove toxic and harmful components in industrial wet-process purified phosphoric acid with high efficiency and low cost and improve the purity of potassium dihydrogen phosphate to meet the requirement of food additive on sanitation and safety is a core technical problem of preparing food-grade potassium dihydrogen phosphate by industrial wet-process purified phosphoric acid and is a fundamental development direction for improving economic benefit in the wet-process phosphoric acid industry.

Disclosure of Invention

Aiming at the defects that monopotassium phosphate prepared by industrial wet-process purified phosphoric acid cannot meet food-grade requirements and the prior art does not have, the invention aims to provide the method for preparing the food-grade monopotassium phosphate, which has the advantages of low cost, high purity, sufficient arsenic and heavy metal ion removal, high sanitary safety, simple and convenient process, high raw material utilization rate, good dissolving performance and mechanized production.

The technical concept of the invention is as follows: the method comprises the steps of utilizing the salting-out effect of barium fluosilicate and barium sulfate precipitates and potassium dihydrogen phosphate which are easily generated by sulfate ions and fluoride ions in industrial wet-process purified phosphoric acid under the weak acid condition to simultaneously carry out defluorination and desulfurization, enabling arsenite to be oxidized into insoluble arsenate, enabling heavy metal ions to generate insoluble precipitates under the neutral alkali condition, neutralizing phosphoric acid into the property that the solubility of potassium dihydrogen phosphate and potassium dihydrogen phosphate with larger solubility changes obviously along with the temperature, diluting the industrial wet-process purified phosphoric acid with water, adding a defluorination and desulfurization agent, carrying out neutralization reaction, carrying out membrane filtration and simultaneously carrying out defluorination and desulfurization on filtrate, oxidizing and dearsenizing by using an oxidant under the weak alkaline condition and precipitating the heavy metal ions, and obtaining the food-grade potassium dihydrogen phosphate through filtration, pH adjustment, concentration, crystallization and drying.

In order to achieve the purpose, the invention adopts the following technical measures:

a method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid is characterized by comprising the following steps:

⑴ adding water to dilute the phosphoric acid, placing the phosphoric acid into an acid-proof container, adding water with the mass multiple of 0.5-3.1 times of the phosphoric acid while stirring to obtain a phosphoric acid diluent with the mass percentage concentration of 20.7-56.7%, and continuously stirring to obtain the phosphoric acid diluent for industrial wet purification.

The industrial wet-process purified phosphoric acid is subjected to defluorination, desulfurization, extraction-back extraction purification treatment and 85% of wet-process phosphoric acid in percentage by mass, and the quality of the industrial wet-process purified phosphoric acid is superior, first-class and qualified products which meet the requirements of HG/T4069-2008 industrial wet-process purified phosphoric acid; the water refers to the conductivity of less than 10^-3s/m reverse osmosis process pure water, ion exchange process pure water, and distillation condensation process pure water.

Preferably, the industrial wet-process purified phosphoric acid is subjected to defluorination, desulfurization and extraction-back extraction purification treatment, and has a mass percentage concentration of 85%, and the mass of the industrial wet-process purified phosphoric acid is a first-class product and a qualified product which meet the requirements of HG/T4069-2008 industrial wet-process purified phosphoric acid; the water isMeans a conductivity of less than 10^-3s/m reverse osmosis pure water.

⑵ neutralization reaction and defluorination and desulfurization, ⑴ of the obtained phosphoric acid diluent is put in an acid-proof container, under the condition of stirring, defluorination and desulfurization agent with the mass fraction of 0.1-1% is added, the stirring is continued, the defluorination and desulfurization agent is fully dissolved and fully reacts with the fluorinion and the sulfate radical in the phosphoric acid diluent, a reaction mixture is obtained, under the condition of stirring, the reaction mixture is neutralized by potassium hydroxide solution with the mass percentage concentration of 20-70% until the pH value is 5.5-7.0, the stirring is continued to obtain a neutralization solution, under the condition that the temperature of the neutralization solution is controlled to be 40-90 ℃, the neutralization solution is precisely filtered by a membrane filtration device, and the obtained precisely filtered neutralization solution is reserved.

The defluorination and desulfurization agent is analytically pure or chemically pure barium carbonate and barium bicarbonate; the potassium hydroxide is analytically pure or chemically pure solid potassium hydroxide; the membrane filtration equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 1, 0.5, 0.1 and 0.04 mu m.

Preferably, the defluorination and desulfurization agent is analytically pure barium carbonate and barium bicarbonate; the potassium hydroxide is analytically pure solid potassium hydroxide; the membrane filtering equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 0.1 and 0.04 mu m.

⑶ oxidizing and dearsenifying, slightly alkaline heavy metal removing and membrane filtering, under the condition of continuously stirring, using a potassium hydroxide solution with the mass percentage concentration of 20-70%, adjusting the pH value of a neutralization solution obtained by ⑵ in the precise filtration to 7.0-8.0, adding an oxidant with the mass fraction of the neutralization solution of 0.1-4%, heating the mixture to the temperature required by arsenic oxidation and maintaining the temperature, refluxing, preserving heat and oxidizing for 0.5-6 hours under the condition of stirring, then opening cooling water to reduce the temperature of the mixture to 40-90 ℃, continuously stirring for 0.5-10 hours, and precisely filtering the mixture by using membrane filtering equipment to obtain the slightly alkaline heavy metal removing and the oxidized dearsenifying solution for later use.

The potassium hydroxide is analytically pure or chemically pure solid potassium hydroxide; the oxidant is analytically pure or chemically pure hydrogen peroxide (hydrogen peroxide) and bleaching powder; the temperature required by the arsenic oxidation is 50-100 ℃; the membrane filtration equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 1, 0.5, 0.1 and 0.04 mu m.

Preferably, the potassium hydroxide is analytically pure solid potassium hydroxide; the oxidant is analytically pure or chemically pure hydrogen peroxide (hydrogen peroxide); the temperature required by the arsenic oxidation is 70-95 ℃; the membrane filtering equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 0.1 and 0.04 mu m.

⑷ adjusting and concentrating the pH of the solution after ⑶ is treated with phosphoric acid to 3.7-4.7 under the condition of continuous stirring to obtain potassium dihydrogen phosphate solution, and concentrating the potassium dihydrogen phosphate solution to 40-55% by mass percentage under the conditions of vacuum degree of 0.8-0.99 MPa and temperature of 70-110 ℃ by a forced circulation vacuum concentration method to obtain potassium dihydrogen phosphate concentrated solution for later use.

The purity of the phosphoric acid is analytically pure, chemically pure and food grade, and the mass percentage concentration of the phosphoric acid is 75% and 85%.

Preferably, the phosphoric acid is food-grade phosphoric acid with a mass percentage concentration of 85%.

⑸ cooling crystallization, transferring the potassium dihydrogen phosphate concentrated solution obtained from ⑷ into crystallization equipment, after crystallizing potassium dihydrogen phosphate within the temperature range of a metastable zone of the potassium dihydrogen phosphate crystal for 1-20 hours, cooling to 1-25 ℃ at the cooling rate of 1-10 ℃/hour, continuing crystallization for 1-40 hours until no crystal is generated, carrying out solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate, and carrying out concentration-crystallization or concentration-spray drying on the crystallized mother solution of potassium dihydrogen phosphate to obtain agricultural potassium dihydrogen phosphate for use as an agricultural potassium phosphate fertilizer, and taking wet potassium dihydrogen phosphate crystal for later use.

The temperature range of the metastable zone of the monopotassium phosphate crystals is 25-60 ℃.

Preferably, the temperature range of the metastable zone of the potassium dihydrogen phosphate crystals is 38-48 DEG C

⑹, drying the crystals, namely drying wet potassium dihydrogen phosphate crystals obtained from ⑸ by hot air at normal pressure until the moisture of the products is required, cooling and packaging to obtain the food-grade potassium dihydrogen phosphate products, wherein the temperature of the materials is controlled to be less than or equal to 100 ℃ in the whole process of the step.

The required moisture content is less than or equal to 1 percent by mass.

Preferably, the water requirement is less than 1% in percentage by mass.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the method mainly solves the separation of tiny solid particles (including pigments) in industrial wet-process purified phosphoric acid by filtering through a silicon carbide film with strong acidity resistance, realizes the precipitation and precipitation of main impurities with large contents of fluorine, sulfur and the like in wet-process diluted phosphoric acid by adding a defluorination and sulfur agent under the condition of subacidity, solves the technical problems and difficulties of the removal of toxic and harmful heavy metals such as arsenic, lead, cadmium and the like in the wet-process diluted phosphoric acid by oxidation dearsenification, alkalescence heavy metal removal and film filtration, and mainly achieves the technical effects of separating impurities, removing toxic and harmful substances and improving the purity of potassium dihydrogen phosphate so that the product meets the food-grade quality requirement. Compared with the prior art, the invention is characterized in that the prior art can only utilize industrial wet-process purified phosphoric acid to prepare the industrial-grade potassium dihydrogen phosphate, and the invention realizes the technical breakthrough of directly preparing the food-grade potassium dihydrogen phosphate by utilizing the industrial wet-process purified phosphoric acid.

2. Through the technical treatment of the invention, the removal rate of insoluble impurities in industrial wet-process purified phosphoric acid is 100 percent, the removal rate of pigments is more than 95 percent, and the appearance is clear and transparent; the removal rate of main impurities such as fluorine ions, sulfur ions (sulfate ions) and the like is more than 99 percent; the removal rate of toxic and harmful substances such as arsenic, lead, cadmium and the like is more than 99.99 percent; the phosphoric acid retention rate is more than 99.5 percent. Through determination, the obtained food-grade monopotassium phosphate is white crystalline powder or particles, and all indexes of the food-grade monopotassium phosphate meet or exceed the requirements of the national food safety standard GB25560-2010 food additive monopotassium phosphate.

3. Low cost, high purity, sufficient removal of arsenic and heavy metal ions, high sanitary safety, simple and convenient process, high utilization rate of raw materials, good solubility, mechanized production and suitability for large-scale and small-scale production.

Drawings

FIG. 1 is a process flow diagram for producing food grade monopotassium phosphate by industrial wet-purification of phosphoric acid according to the present invention.

Detailed Description

The applicant shall now describe the process of the present invention in further detail with reference to specific examples.

Example 1:

a method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid comprises the following steps:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 'industrial wet-process purified phosphoric acid' and 85% industrial wet-process purified phosphoric acid in an acid-proof container, adding pure water with the mass multiple of 1.12 times of that of the industrial wet-process purified phosphoric acid under the condition of stirring, and continuing stirring for 0.5 hour to obtain 40% industrial wet-process purified phosphoric acid diluent, wherein the stirring speed is controlled to be 100rpm in the whole process of the step.

⑵ neutralization and defluorination and desulfurization, 1.5kg of 40% industrial wet-process purified phosphoric acid diluent obtained in step ⑴ is taken and put in an acid-proof container, barium carbonate with the mass fraction of 0.2% is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 5 hours until no bubbles (carbon dioxide) are generated, the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, the reaction mixture is neutralized by 50% of potassium hydroxide solution to the pH value of 6.3, the stirring is continued for 7.5 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled to be 65 ℃, the neutralized solution is precisely filtered by microporous membrane equipment with silicon carbide as a membrane material, the membrane pores are 0.04 mu m and the membrane component form is a honeycomb coal type inner tubular membrane, barium sulfate, barium fluosilicate and other solid particles are separated, and the precisely filtered neutralized solution is prepared for standby.

⑶ oxidizing dearsenification, slightly alkaline heavy metal removal and membrane filtration, under the condition of continuously stirring, using a potassium hydroxide solution with the mass percentage concentration of 50%, adjusting the pH value of the neutralization solution obtained in the step ⑵ to 8.0, adding bleaching powder with the mass fraction of the neutralization solution of 0.5% as an oxidant, heating the mixture to 83 ℃ and maintaining the temperature at 83 ℃, after refluxing, preserving the heat and oxidizing for 3.3 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidizing solution to 65 ℃, continuing to stir for 5.3 hours, precisely filtering the mixture by using microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.04 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the slightly alkaline dearsenification solution and the oxidizing dearsenification solution after precise filtration, wherein the stirring speed is controlled to be 100rpm in the whole process.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.3 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 47.5 wt% potassium dihydrogen phosphate concentrate by rotary evaporation vacuum concentration method under vacuum degree of 0.95MPa and temperature of 95 deg.C, and controlling stirring speed at 150 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 43 ℃ to crystallize potassium dihydrogen phosphate for 10 hours, cooling to 13 ℃ at a cooling rate of 5 ℃/hour, continuing to crystallize for 20 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 1020g of food grade potassium dihydrogen phosphate product.

The food grade potassium dihydrogen phosphate is white crystalline powder or granules; content of potassium dihydrogen phosphate (KH)₂PO₄) (mass percent,%) is not less than 98.0, water-insoluble substances are not more than 0.2, arsenic (As, mg/kg) is not more than 3, heavy metals (mg/kg) is not more than 10, lead (Pb, mg/kg) is not more than 2, fluoride (mg/kg) is not more than 10, pH (10g/L) is 4.2-4.7, and dry weight loss (mass percent,%) is not more than 1.0. All physical and chemical indexes of the food additive meet or exceed the requirements of national food safety standard GB25560-2010 food additive potassium dihydrogen phosphate.

Example 2:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 0.98 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration of 85% into an acid-resistant container under the condition of stirring, continuously stirring for 1.

⑵ neutralization and defluorination and desulfurization 9.83kg of industrial wet-process purified phosphoric acid diluent obtained in step ⑴ is taken, 9.83kg of industrial wet-process purified phosphoric acid diluent is taken, barium carbonate with the mass percentage of 0.3 percent is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 6 hours until no air bubbles (carbon dioxide) are generated, so that the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, the reaction mixture is neutralized by potassium hydroxide solution with the mass percentage of 40 percent until the pH value is 6.5, the stirring is continued for 8 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled at 70 ℃, the neutralized solution is precisely filtered by microporous membrane equipment with a membrane material of silicon carbide, the membrane pores are 0.1 mu m and the membrane component is a honeycomb coal type inner tubular membrane, barium sulfate, barium fluosilicate and other solid particles are separated to obtain the precisely filtered neutralized solution, the stirring speed is controlled at 160rpm in the whole process of the step.

⑶ oxidizing dearsenification, slightly alkaline heavy metal removal and membrane filtration, under the condition of continuously stirring, using a potassium hydroxide solution with the mass percentage concentration of 50%, adjusting the pH value of the neutralization solution obtained in the step ⑵ to 8.0, adding hydrogen peroxide with the mass fraction of the neutralization solution of 0.4% as an oxidant, heating the mixture to 85 ℃ and maintaining the temperature at 85 ℃, after refluxing, preserving the heat and oxidizing for 3.5 hours under the condition of stirring, opening cooling water to reduce the temperature of an oxidizing solution to 70 ℃, continuing to stir for 5.5 hours, precisely filtering the mixture by using microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.1 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the slightly alkaline dearsenification solution and the slightly alkaline dearsenification solution for precise filtration, wherein the stirring speed is controlled to be 120rpm in the whole process.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the obtained heavy metal removal and arsenic removal solution ⑶ to 4.4 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 50 wt% of potassium dihydrogen phosphate under vacuum degree of 0.95MPa and temperature of 100 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 150 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 44 ℃ to crystallize potassium dihydrogen phosphate for 11 hours, cooling to 10 ℃ at the speed of 6 ℃/hour, continuing to crystallize for 22 hours until no crystal is generated, carrying out solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 65 deg.C, 3.5m/s speed and 70% relative humidity until the water content is less than 1%, and cooling to obtain 6.89kg of food-grade potassium dihydrogen phosphate product.

Example 3:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 1.30 times of the mass of the product under the condition of stirring, continuing to stir for 0.5 hour to obtain 37% industrial wet purification phosphoric acid diluent, and controlling the stirring speed to be.

⑵ neutralization and defluorination and desulfurization 3.5kg of 37 wt% industrial wet-process purified phosphoric acid diluent obtained in step ⑴ is put in an acid-proof container, barium carbonate with a mass fraction of 0.4 wt% is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 4.5 hours until no air bubbles (carbon dioxide) are generated, so that the barium carbonate is fully dissolved and fully reacted with fluoride ions and sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, the reaction mixture is neutralized by a potassium hydroxide solution with a mass fraction of 60 wt% to a pH value of 6.0, the stirring is continued for 7 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled at 60 ℃, the neutralized solution is precisely filtered by a microporous membrane device with a membrane material of silicon carbide, a membrane pore diameter of 0.04 mu m and a membrane assembly form of a honeycomb coal type inner tubular membrane, barium sulfate, barium fluorosilicate and other solid particles are separated to obtain the precisely filtered neutralized solution for standby, and the stirring speed is controlled at 140rpm in the whole process.

⑶ oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtration under the condition of continuous stirring, using potassium hydroxide solution with the mass percentage concentration of 60%, adjusting the pH value of the neutralization solution obtained in the step ⑵ to 7.8, adding hydrogen peroxide with the mass fraction of the neutralization solution of 2.5% as oxidant, heating the mixture to 80 ℃ and maintaining the temperature at 80 ℃, after refluxing, preserving heat and oxidizing for 3 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidant to 60 ℃, continuing to stir for 5 hours, precisely filtering the mixture by microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.04 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide and cadmium oxide, and obtaining the slightly alkaline to remove heavy metal and the oxidizing to remove arsenic of the precise filtration, controlling the stirring speed to be 110rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of ⑶ to 4.4 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating by rotary evaporation vacuum concentration method under vacuum degree of 0.96MPa and temperature of 90 deg.C to obtain potassium dihydrogen phosphate concentrated solution with 45.5 wt% concentration, and controlling stirring speed at 160 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 41 ℃ to crystallize potassium dihydrogen phosphate for 9 hours, then cooling to 5 ℃ at a cooling rate of 4 ℃/hour, continuing to crystallize for 23 hours until no crystal is generated, carrying out solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 55 deg.C, 4.5m/s speed and 65% relative humidity until the water content is less than 1%, and cooling to obtain 2.24kg of food-grade potassium dihydrogen phosphate product.

Example 4:

⑴, adding water to dilute, putting qualified products and industrial wet-process purified phosphoric acid with the mass percentage concentration of 85 percent, which meet the requirements of HG/T4069-2008 < industrial wet-process purified phosphoric acid >, into an acid-resistant container, adding reverse osmosis pure water with the mass multiple of 0.85 time under the condition of stirring, and continuously stirring for 1.5 hours to obtain industrial wet-process purified phosphoric acid diluent with the mass percentage concentration of 46 percent, wherein the stirring speed is controlled to be 100rpm in the whole process of the step.

⑵ neutralization and defluorination and desulfurization 1500kg of industrial wet-process purified phosphoric acid diluent with the mass percentage concentration of 46 percent obtained in the step ⑴ is put in an acid-proof container, barium carbonate with the mass percentage of 0.5 percent is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 7 hours until no bubbles (carbon dioxide) are generated, the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent, a reaction mixture is obtained, the stirring is maintained, a potassium hydroxide solution with the mass percentage concentration of 35 percent is used for neutralizing the reaction mixture until the pH value is 6.6, the stirring is continued for 8.5 hours, the neutralization liquid is obtained, the temperature of the neutralization liquid is controlled to be 75 ℃, the neutralization liquid is precisely filtered by a microporous membrane device with the membrane material being silicon carbide, the membrane pores being 0.1 mu m and the membrane component being a honeycomb coal type inner tubular membrane, the barium sulfate, the barium fluorosilicate and other solid particles are separated, the precisely filtered neutralization liquid is obtained, and the stirring speed is controlled to be 170rpm in the whole.

⑶ oxidizing to remove arsenic, removing heavy metal with alkalescence, filtering with membrane, adjusting pH of the neutralized solution obtained in step ⑵ to 7.6 with 35% potassium hydroxide solution by mass percentage, adding hydrogen peroxide with 0.5% of neutralized solution as oxidant, heating the mixture to 90 deg.C, maintaining at 90 deg.C, refluxing under stirring, maintaining the temperature, oxidizing for 4 hr, cooling with water to reduce the temperature of the oxide to 75 deg.C, stirring for 6.5 hr, filtering with microporous membrane equipment with silicon carbide membrane, 0.1 μm membrane pore and honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide and cadmium oxide, and separating the heavy metal with alkalescence and the arsenic removing solution with precision filtration at 130 rpm.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the obtained heavy metal removal and arsenic removal solution ⑶ to 4.2 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 50.9 wt% of potassium dihydrogen phosphate under vacuum degree of 0.95MPa and temperature of 90 deg.C by forced circulation vacuum concentration method, and controlling stirring speed at 160 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 42 ℃ to crystallize potassium dihydrogen phosphate for 12 hours, cooling to 10 ℃ at a cooling rate of 3.5 ℃/hour, continuing to crystallize for 25 hours until no crystals are generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystals and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which is used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystals for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 783.4kg of food-grade potassium dihydrogen phosphate product.

Example 5:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 1.43 times of the mass of the phosphoric acid into the acid-resistant container under the condition of stirring, and continuing stirring for 0.5 hour to obtain industrial wet purification phosphoric acid diluent with the mass.

⑵ neutralization and defluorination and desulfurization 4.5kg of 35 wt% industrial wet-process purified phosphoric acid diluent obtained in step ⑴ is put in an acid-proof container, barium carbonate with the mass fraction of 0.2 wt% is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 5.5 hours until no air bubbles (carbon dioxide) are generated, so that the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, the reaction mixture is neutralized by 55 wt% potassium hydroxide solution until the pH value is 5.9, the stirring is continued for 6.5 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled to be 55 ℃, the neutralized solution is precisely filtered by microporous membrane equipment with a membrane material of silicon carbide, a membrane pore diameter of 0.04 mu m and a membrane assembly form of a honeycomb coal type inner tubular membrane, barium sulfate, barium fluorosilicate and other solid particles are separated to obtain the precisely filtered neutralized solution for standby, and the stirring speed is controlled to be 140rpm in the whole process.

⑶ oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtration under the condition of continuous stirring, using 55% potassium hydroxide solution by mass percentage concentration, adjusting the pH of the neutralization solution obtained in the step ⑵ to 7.4, adding hydrogen peroxide with the mass fraction of the neutralization solution being 0.4% as oxidant, heating the mixture to 78 ℃ and maintaining the temperature at 78 ℃, after refluxing, preserving heat and oxidizing for 4.5 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidant to 50 ℃, continuing to stir for 6 hours, precisely filtering the mixture by microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.04 mu m and a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the slightly alkaline to remove heavy metal and oxidizing to remove arsenic by membrane filtration, wherein the stirring speed is 100rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.1 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 45.5 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 160 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 40 ℃ to crystallize potassium dihydrogen phosphate for 13 hours, cooling to 10 ℃ at a cooling rate of 5 ℃/hour, continuing to crystallize for 24 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 2.69kg of food-grade potassium dihydrogen phosphate product.

Example 6:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 0.77 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration into the acid-resistant container under the condition of stirring, and continuously stirring for 1.5.

⑵ neutralization reaction and defluorination and desulfurization, getting 650g of 48% industrial wet-process purified phosphoric acid diluent obtained in step ⑴, adding barium carbonate with the mass fraction of 0.5% as defluorination and desulfurization agent under the condition of continuous stirring, continuing stirring for 8 hours until no bubbles (carbon dioxide) are generated, fully dissolving the barium carbonate and fully reacting with the fluorine ions and sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, maintaining stirring, neutralizing the reaction mixture with 40% potassium hydroxide solution to the pH value of 6.5, continuing stirring for 9 hours to obtain a neutralized solution, controlling the temperature of the neutralized solution to 70 ℃, precisely filtering the neutralized solution by a device with a membrane material of silicon carbide, a membrane hole of 0.1 μm and a membrane component of a honeycomb coal type inner tubular membrane, separating barium sulfate, barium fluorosilicate and other solid particles to obtain the precisely filtered neutralized solution, and controlling the stirring speed to be 165rpm in the whole process.

⑶ oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtration under the condition of continuous stirring, using potassium hydroxide solution with the mass percentage concentration of 40%, adjusting the pH value of the neutralization solution obtained in the step ⑵ to 8.0, adding hydrogen peroxide with the mass fraction of the neutralization solution of 0.6% as oxidant, heating the mixture to 90 ℃ and maintaining the temperature at 90 ℃, after refluxing, preserving heat and oxidizing for 3 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidant to 55 ℃, continuing to stir for 7 hours, precisely filtering the mixture by microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.1 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide and cadmium oxide, and the like to obtain the slightly alkaline to remove heavy metal and the oxidizing to remove arsenic of the precise filtration, and controlling the stirring speed to be 130rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the obtained heavy metal removal and arsenic removal solution ⑶ to 4.2 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 45.5 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 120 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 39 ℃ to crystallize potassium dihydrogen phosphate for 14 hours, cooling to 10 ℃ at a cooling rate of 3 ℃/hour, continuing to crystallize for 20 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain food grade potassium dihydrogen phosphate product 520 g.

Example 7:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt & lt & gt, adding reverse osmosis pure water with the mass multiple of 1.80 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration of 85% into an acid-resistant container under the condition of stirring.

⑵ neutralization and defluorination and desulfurization, 5.68kg of industrial wet-process purified phosphoric acid diluent with the mass percentage concentration of 30.4 percent obtained in the step ⑴ is taken in an acid-proof container, barium carbonate with the mass percentage of 0.18 percent is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 5.5 hours until no bubbles (carbon dioxide) are generated, the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, potassium hydroxide solution with the mass percentage concentration of 65 percent is used for neutralizing the reaction mixture until the pH value is 6.7, the stirring is continued for 9 hours to obtain a neutralized liquid, the temperature of the neutralized liquid is controlled at 70 ℃, the neutralized liquid is precisely filtered by a microporous membrane device with a membrane material of silicon carbide, a membrane pore diameter of 0.04 mu m and a membrane assembly form of a honeycomb coal type inner tubular membrane, barium sulfate, barium fluorosilicate and other solid particles are separated to obtain the precisely filtered neutralized liquid for standby, and the stirring speed is controlled at 110rpm in the whole process of.

⑶ oxidizing dearsenification, slightly alkaline heavy metal removal and membrane filtration, under the condition of continuously stirring, using 65 mass percent potassium hydroxide solution to adjust the pH of the neutralized liquid obtained in the step ⑵ to 7.5, adding hydrogen peroxide with the mass fraction of the neutralized liquid being 0.3 percent as an oxidant, heating the mixture to 85 ℃ and maintaining the temperature at 85 ℃, after refluxing, preserving the heat and oxidizing for 4.3 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxide liquid to 50 ℃, continuing to stir for 6.3 hours, precisely filtering the mixture by microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.04 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the slightly alkaline dearsenification and oxidation liquid for later use, wherein the stirring speed is 90rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.25 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 48.5 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 140 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 40.5 ℃ to crystallize potassium dihydrogen phosphate for 13 hours, cooling to 5 ℃ at a cooling rate of 3.5 ℃/hour, continuing to crystallize for 27 hours until no crystal is generated, carrying out solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a mother solution for potassium dihydrogen phosphate crystal (the mother solution for potassium dihydrogen phosphate crystal can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 3.13kg of food-grade potassium dihydrogen phosphate product.

Example 8:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 0.70 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration of 85% into an acid-resistant container under the condition of stirring, continuously stirring for 0.

⑵ neutralization and defluorination and desulfurization 2.45kg of 50% diluted solution of industrial wet-process purified phosphoric acid obtained in step ⑴ is taken in an acid-proof container, barium bicarbonate with the mass fraction of 0.5% is added as defluorination and desulfurization agent under the condition of continuous stirring, stirring is continued for 4 hours until no bubbles (carbon dioxide) are generated, so that the barium bicarbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the diluted solution of phosphoric acid to obtain a reaction mixture, stirring is maintained, the reaction mixture is neutralized to the pH of 6.9 by 45% potassium hydroxide solution, stirring is continued for 8.5 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled at 50 ℃, the neutralized solution is precisely filtered by microporous membrane equipment with silicon carbide, the membrane pores are 0.1 mu m and the membrane component is a honeycomb coal type inner tubular membrane, barium sulfate, barium fluosilicate and other solid particles are separated to obtain the precisely filtered neutralized solution, and the stirring speed is controlled at 160rpm in the whole process of the step.

⑶ oxidizing to remove arsenic, removing heavy metal with alkalescence, filtering with membrane, adjusting pH of the neutralized solution obtained in step ⑵ to 8.0 with 45% potassium hydroxide solution by mass percentage under the condition of continuous stirring, adding hydrogen peroxide with 2.05% of neutralized solution by mass as oxidant, heating the mixture to 80 ℃ and maintaining the temperature at 80 ℃, refluxing under the condition of stirring, keeping the temperature and oxidizing for 4 hours, opening cooling water to reduce the temperature of the oxidant to 55 ℃, continuing to stir for 6.6 hours, precisely filtering with microporous membrane equipment with membrane material of silicon carbide, membrane pores of 0.1 μm and inner tubular membrane of honeycomb briquette type, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide and cadmium oxide, and obtaining alkalescent heavy metal and arsenic removing solution with precision filtration, controlling the stirring speed to be 110rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.1 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 49.5 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 140 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 40 ℃ to crystallize potassium dihydrogen phosphate for 11 hours, cooling to 5 ℃ at a cooling rate of 3 ℃/hour, continuing to crystallize for 24 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 2.22kg of food-grade potassium dihydrogen phosphate product.

Example 9:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt & lt & gt, adding reverse osmosis pure water with the mass multiple of 3.1 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration of 85% into an acid-resistant container under the condition of stirring.

⑵ neutralization and defluorination and desulfurization 3.25kg of industrial wet-process purified phosphoric acid diluent with the mass percentage of 20.7 percent obtained in the step ⑴ is taken in an acid-proof container, barium carbonate with the mass percentage of 0.19 percent is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 3 hours until no air bubbles (carbon dioxide) are generated, so that the barium carbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, the stirring is maintained, the reaction mixture is neutralized by potassium hydroxide solution with the mass percentage of 70 percent until the pH value is 6.5, the stirring is continued for 9 hours to obtain a neutralized solution, the temperature of the neutralized solution is controlled to be 55 ℃, the neutralized solution is precisely filtered by microporous membrane equipment with a membrane material of silicon carbide, the membrane pores are 0.1 mu m and the membrane component is a honeycomb coal type inner tubular membrane, barium sulfate, barium fluosilicate and other solid particles are separated to obtain the precisely filtered neutralized solution, the stirring speed is controlled to be 125rpm in the whole process.

⑶ oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtering, under the condition of continuously stirring, using 70% potassium hydroxide solution by mass percentage concentration, adjusting the pH of the neutralized liquid obtained in the step ⑵ to 7.9, adding hydrogen peroxide with 0.3% of the neutralized liquid by mass fraction as oxidant, heating the mixture to 80 ℃ and maintaining the temperature at 80 ℃, after refluxing, preserving heat and oxidizing for 4.5 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidant to 45 ℃, continuing stirring for 6 hours, precisely filtering the mixture by using microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.1 mu m and a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the slightly alkaline to remove heavy metal and oxidizing to remove arsenic by membrane filtration, controlling the stirring speed to be 90rpm in the whole process of the step.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.15 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 49.6 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by rotary evaporation vacuum concentration method, and controlling stirring speed at 135 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 40.5 ℃ to crystallize potassium dihydrogen phosphate for 11 hours, cooling to 10 ℃ at a cooling rate of 5 ℃/hour, continuing to crystallize for 23 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a mother solution for potassium dihydrogen phosphate crystal (the mother solution for potassium dihydrogen phosphate crystal can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal by wet crystallization of potassium dihydrogen phosphate obtained in step ⑸ with hot air at 60 deg.C, speed of 3m/s and relative humidity of 75%, drying until the water content is less than 1%, and cooling to obtain 1.07kg of food-grade potassium dihydrogen phosphate product.

Example 10:

⑴, adding water to dilute, putting qualified products with the quality meeting the requirements of HG/T4069-2008 & ltIndustrial Wet purification phosphoric acid & gt 2008 & lt & gt, adding reverse osmosis pure water with the mass multiple of 0.50 times of the mass of the qualified products and the industrial wet purification phosphoric acid with the mass percentage concentration of 85% into an acid-resistant container under the condition of stirring, continuously stirring for 1.5.

⑵ neutralization and defluorination and desulfurization 500kg of industrial wet-process purified phosphoric acid diluent with the mass percentage concentration of 56.7 percent obtained in the step ⑴ is put in an acid-proof container, barium bicarbonate with the mass percentage of 1.0 percent is added as a defluorination and desulfurization agent under the condition of continuous stirring, the stirring is continued for 4 hours until no bubbles (carbon dioxide) are generated, the barium bicarbonate is fully dissolved and fully reacted with the fluorine ions and the sulfate radicals in the phosphoric acid diluent, a reaction mixture is obtained, the stirring is maintained, a potassium hydroxide solution with the mass percentage concentration of 30 percent is used for neutralizing the reaction mixture until the pH value is 6.8, the stirring is continued for 7 hours, the neutralization solution is obtained, the temperature of the neutralization solution is controlled to be 55 ℃, the neutralization solution is precisely filtered by a microporous membrane device with the membrane material of silicon carbide, the membrane pores of 0.04 mu m and the membrane component form of a honeycomb coal type inner tubular membrane, barium sulfate, barium fluorosilicate and other solid particles are separated, the precisely filtered neutralization solution is obtained for standby, and the stirring speed is controlled to be 145rpm in.

⑶ oxidizing dearsenification, slightly alkaline heavy metal removal and membrane filtration, under the condition of continuously stirring, using 30 mass percent potassium hydroxide solution to adjust the pH of the neutralized liquid obtained in the step ⑵ to 7.9, adding hydrogen peroxide with the mass fraction of the neutralized liquid being 4.0 percent as an oxidant, heating the mixture to 90 ℃ and maintaining the temperature at 90 ℃, after refluxing, preserving the heat and oxidizing for 3.5 hours under the condition of stirring, opening cooling water to reduce the temperature of the oxidized liquid to 50 ℃, continuing to stir for 6 hours, precisely filtering the mixture by microporous membrane equipment with a membrane material of silicon carbide, a membrane hole of 0.04 mu m and a membrane component of a honeycomb coal type inner tubular membrane, separating insoluble substances such as barium arsenate, potassium arsenate, lead oxide, cadmium oxide and the like, and obtaining the precisely filtered slightly alkaline heavy metal removal and the oxidized dearsenification solution for standby.

⑷ adjusting pH and concentrating under stirring, adjusting pH of the alkalescent heavy metal and arsenic removing oxide solution obtained in step ⑶ to 4.35 with 85 wt% edible phosphoric acid to obtain potassium dihydrogen phosphate solution, concentrating the potassium dihydrogen phosphate solution to 48.6 wt% potassium dihydrogen phosphate concentrate under vacuum degree of 0.95MPa and temperature of 95 deg.C by forced circulation vacuum concentration method, and controlling stirring speed at 135 rpm.

⑸ cooling and crystallizing, transferring the potassium dihydrogen phosphate concentrated solution obtained in step ⑷ into a crystallizing device, cooling to 40 ℃ to crystallize potassium dihydrogen phosphate for 13 hours, cooling to 5 ℃ at a cooling rate of 5 ℃/hour, continuously crystallizing for 24 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet potassium dihydrogen phosphate crystal and a crystallized mother solution of potassium dihydrogen phosphate (the crystallized mother solution of potassium dihydrogen phosphate can be concentrated-crystallized or concentrated-spray dried to obtain agricultural potassium dihydrogen phosphate which can be used as an agricultural potassium phosphate fertilizer), and taking wet potassium dihydrogen phosphate crystal for later use.

⑹ drying crystal, namely drying wet potassium dihydrogen phosphate crystal obtained in step ⑸ by hot air with the temperature of 60 ℃, the speed of 3m/s and the relative humidity of 75% until the mass percentage of water is less than 1%, and cooling to obtain 512.5kg of food-grade potassium dihydrogen phosphate product.

The specific embodiments described in this specification are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims

1. A method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid is characterized by comprising the following steps:

⑴ adding water for dilution, putting the industrial wet-process purified phosphoric acid into an acid-resistant container, adding water with the mass multiple of 0.5-3.1 times of that of the industrial wet-process purified phosphoric acid under the condition of stirring to obtain a phosphoric acid diluent with the mass percentage concentration of 20.7-56.7%, and continuously stirring to obtain the industrial wet-process purified phosphoric acid diluent;

⑵ performing neutralization reaction and defluorination and desulfurization, namely putting a phosphoric acid diluent obtained in ⑴ into an acid-resistant container, adding a defluorination and desulfurization agent with the mass fraction of 0.1-1% of the phosphoric acid diluent under the condition of stirring, continuously stirring to ensure that the defluorination and desulfurization agent are fully dissolved and fully reacted with fluoride ions and sulfate radicals in the phosphoric acid diluent to obtain a reaction mixture, neutralizing the reaction mixture by using a potassium hydroxide solution with the mass percentage concentration of 20-70% under the condition of stirring until the pH value is 5.5-7.0, and continuously stirring to obtain a neutralization solution, precisely filtering the neutralization solution by using membrane filtration equipment under the condition of controlling the temperature of the neutralization solution to be 40-90 ℃, and keeping the obtained precisely filtered neutralization solution for later use;

⑶, oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtering, under the condition of continuously stirring, adjusting the pH of the neutralized liquid obtained by precise filtering with ⑵ to 7.0-8.0 by using a potassium hydroxide solution with the mass percentage concentration of 20-70%, adding an oxidant with the mass fraction of 0.1-4% of the neutralized liquid, heating the mixture and maintaining the temperature of the mixture to the temperature required by arsenic oxidation, refluxing, preserving heat and oxidizing for 0.5-6 hours under the condition of stirring, then opening cooling water to reduce the temperature of the mixture to 40-90 ℃, continuously stirring for 0.5-10 hours, and precisely filtering the mixture by using membrane filtering equipment to obtain the slightly alkaline to remove heavy metal and the oxidized arsenic-removing liquid for later use;

⑷, under the condition of continuous stirring, the pH of the alkalescent heavy metal removal and oxidation dearsenization solution obtained by ⑶ is adjusted to 3.7-4.7 by phosphoric acid to obtain potassium dihydrogen phosphate solution, and the potassium dihydrogen phosphate solution is concentrated to 40-55% by mass percentage concentration by a forced circulation vacuum concentration method under the conditions of a vacuum degree of 0.8-0.99 MPa and a temperature of 70-110 ℃ to obtain potassium dihydrogen phosphate concentrated solution for later use;

⑸ cooling crystallization, namely transferring the potassium dihydrogen phosphate concentrated solution obtained by ⑷ into crystallization equipment, after crystallizing potassium dihydrogen phosphate within the temperature range of a metastable zone of the potassium dihydrogen phosphate crystal for 1-20 hours, reducing the temperature to 1-25 ℃ at the cooling speed of 1-10 ℃/hour, and continuously crystallizing for 1-40 hours until no crystal is generated;

2. The method for producing food grade potassium dihydrogen phosphate with industrial wet-process purified phosphoric acid as claimed in claim 1, wherein said step ⑴ is implementedThe industrial wet-process purified phosphoric acid is subjected to defluorination, desulfurization, extraction-back extraction purification treatment and 85% of wet-process phosphoric acid by mass percentage, and the quality of the industrial wet-process purified phosphoric acid is superior, first-class and qualified products which meet the requirements of HG/T4069-2008 industrial wet-process purified phosphoric acid; the water refers to the conductivity of less than 10^-3s/m reverse osmosis process pure water, ion exchange process pure water, and distillation condensation process pure water.

3. The method for preparing food-grade potassium dihydrogen phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein said defluorinating agent in step ⑵ is analytically or chemically pure barium carbonate or barium bicarbonate, said potassium hydroxide is analytically or chemically pure solid potassium hydroxide, said membrane filtration equipment has a membrane material of silicon carbide, said membrane component is in the form of a honeycomb-coal-type inner tubular membrane, and said membrane has a pore size of 1, 0.5, 0.1 or 0.04 μm.

4. The method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein the potassium hydroxide in step ⑶ is analytically or chemically pure solid potassium hydroxide, the oxidants are analytically or chemically pure hydrogen peroxide (hydrogen peroxide) and bleaching powder, the temperature required by arsenic oxidation is 50-100 ℃, and the membrane material of the membrane filtration equipment is silicon carbide, the membrane component is a honeycomb coal type inner tubular membrane, and the size of the membrane pores is 1, 0.5, 0.1 or 0.04 μm.

5. The method for producing food grade potassium dihydrogen phosphate by using industrial wet-purification phosphoric acid as claimed in claim 1, wherein said phosphoric acid in step ⑷ has a purity of analytical grade, chemical grade or food grade.

6. The method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein the metastable zone temperature of monopotassium phosphate crystals in the step ⑸ is 25-60 ℃.

7. The method for preparing food-grade monopotassium phosphate by using industrial wet-process purified phosphoric acid as claimed in claim 1, wherein the required moisture content in step ⑹ is less than or equal to 1% by mass.